None.
Not Applicable.
The present invention relates generally to vehicle wheel alignment, and specifically to a method for calibrating wheel alignment sensors or optical targets for use with no-compensation and universal wheel adapters, and for the detection and correction of wear or damage to the non-compensation or universal wheel adapters to which the wheel alignment sensors or optical targets are attached during a vehicle wheel alignment procedure.
Conventional wheel alignment systems typically utilize one of two types of wheel adapters to attach alignment sensors or optical targets to each wheel of a vehicle being measured. The first of these, seen in FIG. 1, is referred to as a universal wheel adapter, and is designed to be electronically compensated for runout during each use by rotating the vehicle wheel through a number of different positions and calculating runout from measurements taken at each position. These wheel adapters do not position the alignment sensors or optical targets in any predetermined orientation to the vehicle wheel, but rather, require that the orientation of the wheel alignment sensors or optical target be determined after placement on adapters. In order to determine the orientation of the wheel alignment sensor or optical target relative to the axis of rotation of the wheel, a procedure known as xe2x80x9ccompensationxe2x80x9d or xe2x80x9crunout compensationxe2x80x9d must be performed. This procedure requires that the wheel (and wheel adapter) be rotated to at least two known positions (typically 180 degrees apart) and that measurements be taken by the alignment sensor or of the optical target at each position. These measurements are then analyzed, and the orientation of the alignment sensor or optical target relative to the axis of rotation of the wheel is determined. This compensates for any differences in orientation between the alignment sensor or optical target and the axis of rotation of the vehicle wheel caused by one or more sources of error. These sources of error include: the indeterminate mounting of the adapter to the wheel; the indeterminate nature of the position and orientation of the features on the alignment adapter support the adapter components, and the points at which the adapter contacts the vehicle wheel.
The second type of wheel adapter, seen in FIGS. 2A and 2B is termed a no-compensation wheel adapter, and is designed to work without the need for any electronic runout compensation. This second type of wheel adapter operates on the assumption that the runout of the vehicle wheel is negligible, and that the manufacturing process of the wheel adapter itself does not induce any additional runout in the system, hence there is no need to rotate the vehicle wheel to different positions to compensate for runout within the system. These no-compensation wheel adapters are configured to minimize orientation errors. By configuring the wheel adapter to contact a vehicle wheel (or other suspension component) in a reliable and repeatable manner, and by choosing points on the vehicle wheel (or other suspension component) that provide a reference which closely represents that plane of rotation of the vehicle wheel, mounting errors incurred by the wheel adapter can be minimized. Similarly, by fabricating the sensor shaft upon which the alignment sensor or optical target is supported by the wheel adapter to be as straight as possible, or at a known angle, as is described in co-pending U.S. patent application Ser. No. 09/196,008, now U.S. Pat. No. 6,134,792 or by calibrating the alignment sensor with the sensor shaft in a fixed position (i.e. in a position wherein rotation is prevented), it is possible to minimize (or theoretically eliminate) any errors due to a lack of straightness in the sensor shaft. Finally, careful fabrication of the wheel adapter itself to minimal tolerances can minimize any position and orientation errors between the sensor shaft mounting points on the wheel adapter and the wheel adapter contact points on the vehicle wheel (or other suspension component).
If all of the above requirements are achieved to a sufficient degree of accuracy (i.e. either electronic runout compensation or minimal manufacturing tolerances), then a conventional wheel alignment system is capable of providing wheel alignment measurements to within the tolerances required for wheel alignment adjustment. However, maintaining these wheel alignment systems in such a serviceable condition and at such tolerances is not always possible, and, in fact, the current condition of a wheel alignment system is not easily determined.
Determination of the condition of a wheel alignment system can be accomplished by evaluating the system as a whole, or by determining the condition of each of the components separately to see if they fall within predetermined specifications. When checking the individual components separately, the condition of the sensor shaft, upon which the alignment sensor or optical target is hung from the wheel adapter, is determined by rotating the sensor shaft and measuring its runout using a dial indicator or similar measuring instrument. Next, in order to assess the condition of a wheel adapter, the orientation of the sensor mounting points on the wheel adapter must be measured relative to the contact points at which the wheel adapter is secured to the vehicle wheel. For a typical wheel adapter, this is determined by measuring the perpendicularity of the sensor shaft mounting point relative to the plane containing the wheel adapter contact points, i.e. determining the relative position of each of the contact points in a direction parallel to the axis of the sensor shaft mounting point. If all of these points are at the same relative position along this axis, then the plane through them is normal to the axis.
A second solution to determining the condition of a wheel alignment system is to provide a means for eliminating any excessive variation of in the geometry of the sensor shaft and the wheel adapter, or by providing a means for accounting for such variation. If the wheel alignment sensor is calibrated by methods known in the art with the sensor shaft in the position in which it is intended to be used, the degree of straightness of the shaft is accounted for, and a separate determination of the runout of the sensor shaft is not necessary. However, this is an acceptable solution only in the case where the shaft can remain in the same fixed position during both the calibration process and its use in a wheel alignment procedure, i.e. the sensor is calibrated in same state in which it will be used.
Among the several objects and advantages of the present invention are:
The provision of a method for compensating for wheel adapter variations associated with wear and damage in no-compensation type wheel adapters wherein the shaft mount axis for receiving a wheel alignment sensor or optical target is adjusted to a predetermined orientation;
The provision of the aforementioned method wherein any condition occurring in the no-compensation wheel adapter which causes the shaft mount axis to be aligned other than normal to the plane containing the contact points for the adapter is compensated for;
The provision of the aforementioned method wherein the contact points of the no-compensation adapter are adjusted in a direction generally parallel to the shaft mount axis until the contact points define a plane perpendicular to the shaft mount axis;
The provision of the aforementioned method wherein the contact points are telescoping, and are adjusted either by extension or retraction;
The provision of the aforementioned method wherein the contact points are threaded, and are adjusted by rotation;
The provision of the aforementioned method wherein the no-compensation wheel adapter is mounted to a shaft arranged perpendicular to a reference surface, and the contact points of the no-compensation adapter are adjusted to contact the reference surface;
The provision of the aforementioned method wherein a reference surface is machined onto the no-compensation adapter to be normal to the sensor mount axis, and the contact points are adjusted to be equidistant from the machined reference surface;
The provision of the aforementioned method utilizing a fixed calibration surface including a flat plate; and
The provision of the aforementioned method wherein more than three contact points are utilized by the no-compensation wheel adapter to define a contact plane, the contact plane utilized to identify wear or damage to the no-compensation wheel adapter as well as the detection of damage to vehicle wheel rims to which the no-compensation wheel adapter is mounted.
The provision of a method for electronically calibrating a vehicle wheel alignment sensor for use with either a no-compensation or a universal wheel adapter wherein calibration values for each type of wheel adapter are stored electronically.
Briefly stated, the present invention relates to the calibration of vehicle wheel alignment sensors and to the detection and correction of wear or damage to no-compensation type wheel adapters to which vehicle wheel alignment sensors or optical targets are attached during a vehicle wheel alignment procedure. When performing vehicle wheel alignments, sources of error include variations in the vehicle wheel alignment sensors, optical targets, and in the mounting of the vehicle wheel adapters to which the wheel alignment sensors are attached. Wheel alignment sensors are calibrated differently depending upon whether they are utilized with universal wheel adapters or with no-compensation type wheel adapters. Accordingly, one aspect of the present invention is a method for electronically storing separate calibration values in a memory associated with a vehicle wheel alignment sensors for both types of vehicle wheel adapters. A second aspect of the present invention is a method and apparatus for detecting and compensating for wear or damage to no-compensation type wheel adapters. By utilizing a known flat reference surface, any misalignment of the sensor mounting shaft axis from the plane defined by the contact points of the wheel adapter may be detected and corrected for, either by adjustment of the contact points or by adjustment of the sensor mounting shaft hub. An additional aspect of the present invention is the inclusion of more than three contact points on a wheel adapter. Utilizing more than three contact points facilitates detection of damage or wear to the wheel adapter by providing a visual indication of the damage or wear when the wheel adapter is placed on a flat surface. Similarly, the use of more than three contact points will provide a visual indication of damage to the rim of a vehicle wheel in the event that not all of the contact points engage the wheel rim surface.
The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.